In an electric car or a hybrid car and the like, a distributive conductor for distributing electric power from an inverter to a motor for running the vehicle to be shielded. A shielded distributive conductor having a structure that collectively shields a plurality of non-shielded wires by enclosing them in a shielding member or braided wires, which is formed by braiding thin metallic wires into a mesh tubular shape, has been practically realized. Such a distributive conductor configured to be shielded with braided wires, however, has a problem because it is necessary to enclose the entire distributive conductor in a protector made of resin in order to protect the braided wires and the insulated wires, which results in an increase in the number of parts and assembling steps because of use of the protector.
The applicants of the present application thus proposed a structure to insert non-shielded wires into a metal pipe, as described in Japanese Patent Application No. 2004-171952. According to this structure, the pipe is effective in a shielding function for the wires and in a protecting function for the wires. This structure thus has the advantage over the structure of the shielded distributive conductor using braided wires and a protector in that it needs less number of parts.
The distributive conductor having a pipe and insulated wires inserted therein, however, cannot avoid intervention of air space between the insulated wires and the pipe. Thus, heat generated when electric current flows through the wires is insulated by the air, which has low thermal conductivity, and is difficult to be transferred to the pipe. Furthermore, since the pipe has no air pathway for accessing the interior with the exterior, which braided wires would have between the mesh, heat generated in the wires tends to be stored inside the pipe and heat dissipation tends to be low.
As a predetermined current is passed through a conductor, the larger cross-sectional area of a conductor allows for minor heat generation. On the other hand, the higher heat dissipation of a conductor allows for minor temperature increase value of the conductor caused by heat generation. Accordingly, in an environment where an upper limit is provided for temperature increase value of a conductor, the cross-sectional area of the conductor in such a shielded distributive conductor of lower heat dissipation efficiency (as explained above) should be large so that the heat generation is minor.
Enlargement of the cross-sectional area of the conductor, however, means enlargement in diameter and weighting of the shielded distributive conductor. Some countermeasure thus becomes necessary.
Thus, there is a need in the art for an improved heat dissipation of a shielded distributive conductor using a pipe.